Experimental and Numerical Investigation of a Carbon Nanotube Acoustic Absorber

326 Pages·2016·20.06 MB·English

by  Md. Ayub

Experimental and Numerical
Investigation of a Carbon Nanotube
Acoustic Absorber
d yub
M . A
School of Mechanical Engineering
The University of Adelaide
South Australia 5005
Australia
Athesissubmittedinfulfilmentofthe
requirementsforthedegreeofPh.D.in
Engineeringonthe14thofOctober2015.
Ph.D.Thesis
Submittedversion
14thofOctober2015
Acoustics,VibrationsandControlGroup
SchoolofMechanicalEngineering
TheUniversityofAdelaide
SouthAustralia5005
Australia
TypesetbytheauthorusingLATEX.
PrintedinAustralia.
Copyright©2016,TheUniversityofAdelaide,SouthAustralia.
Allrightreserved.Nopartofthisreportmaybeusedorreproducedinanyformor
byanymeans,orstoredinadatabaseorretrievalsystemwithoutpriorwritten
permissionoftheuniversityexceptinthecaseofbriefquotationsembodiedin
criticalarticlesandreviews.
Summary
Theinterestinapplicationsofnanomaterialsforacousticabsorptionpurposes
is growing rapidly with advances in nanotechnology. A need also exists for
a simulation framework that is applicable for modelling acoustic absorp-
tion in nanomaterials in order to develop an understanding of nanoscopic
acoustic absorption mechanisms. The current study investigates the acoustic
absorption characteristics of a carbon nanotube (CNT) acoustic absorber to
develop an understanding of the absorption behaviour and mechanisms of
the CNTs. This task involves undertaking an exploratory study of the absorp-
tion characteristics of a CNT forest and modelling the absorption effects of
the CNT at the nanoscale. The absorption characteristics of the CNTs were
explored by studying the normal incidence absorption coefficient of 3mm-
and 6mm-long vertically aligned CNT arrays measured experimentally us-
ing the two-microphone impedance tube method, while the modelling of
the absorption effects was performed using a non-continuum particle-based
method. The experimental investigation showed promising results for the
acoustic absorption capability of CNT acoustic absorbers and suggests that
theabsorptionperformancecouldbeenhancedwithlongerCNTsandalower
spatial density of the nanotube arrays. The study of absorption using a theo-
retical model based on classical absorption mechanisms indicated that the
absorption behaviour of nanomaterials is likely to deviate from continuum
behaviour emphasising the necessity of acoustic modelling at the nanoscale
using non-continuum methods. An examination of the physical phenomena
that are likely to be relevant for simulating acoustic wave propagation in the
presence of CNTs revealed that the modelling of such a system would be a
multi-physics problem involving heat transfer and dynamic interaction of
particle vibrations. A study of various particle approaches of non-continuum
methods indicated that molecular dynamics (MD) is the method best suited
to simulate and study the acoustic absorption of CNTs at the nanoscale. A
survey of previous molecular simulations demonstrated that the MD simula-
tions carried out thus far have not simultaneously accounted for all relevant
i
ii Summary
aspects of the multi-physics problem required for modelling the acoustic
absorptioneffectsofCNTs.Hence,threeindependentvalidationstudieswere
performed using MD simulations for modelling a subset of the relevant phe-
nomena, namely fluid/structure interactions, bi-directional heat transfer, and
acoustic wave propagation. Each of these MD simulations were performed
for a model incorporating Lennard-Jones (LJ) potentials for the non-bonded
interactions of gas and CNT atoms and the REBO potential for the CNT, and
the results validated against the reference case studies.
A molecular system was then designed to study acoustic wave propaga-
tion in a simple monatomic gas in a domain containing a 50nm-long CNT
oppositetothesoundsourceandparalleltothedirectionoftheacousticwave
propagation. The simulation domain was modelled using argon gas as the
wave propagation medium, a piston made of solid argon layers as a sound
source, and a specular wall as the termination wall. MD simulations were
also performed without the CNT present for comparison. The characteristics
of the acoustic field were studied by evaluating the behaviour of various
acoustic parameters and comparing the change in behaviour with frequency.
The attenuation of the acoustic wave was estimated using thermodynamic
exergy concepts and compared against standing wave theory and predictions
fromcontinuummechanics.Similarly,theacousticfieldcharacteristicsandat-
tenuation due to the CNT were studied using MD simulations incorporating
the CNT. A standing wave model, developed for the domain with the CNT
present, was used to predict the attenuation by the CNT and verified against
estimates from exergy concepts. Comparison of the simulation results for
acoustic wave propagation with and without the CNT present demonstrated
that acoustic absorption effects in the presence of CNTs can be simulated
using the developed MD simulation setup although the degree of absorption
was not sufficient for the CNTs simulated to investigate absorption mecha-
nisms. The modelled MD system can also be used to study deviations from
continuum theory in the characteristics of high frequency sound. The study
suggests that the investigation of absorption mechanisms in nanomaterials
canbeconductedusingthedevelopedplatformforMDsimulations,however
further investigations are required to capture the loss mechanisms involved
in the molecular interactions between the acoustic wave and the CNT. Addi-
tionally, to permit simulations in the audible frequency range, it is necessary
to speed up the computational process by modifying the system model such
as by employing a hybrid model with molecular dynamics coupled to a
continuum domain.
Declarations
Originality
Thisworkcontainsnomaterialwhichhasbeenacceptedfortheawardofany
other degree of diploma in any university or other tertiary institution. To the
best of my knowledge and belief, this work contains no material previously
published orwritten byanother person, exceptwhere due referencehas been
made in the text.
Permissions
I give consent to this copy of my thesis, when deposited in the University
Library, being made available for loan and photocopying, subject to the
provisions of the Copyright Act 1968.
I also give permission for the digital version of my thesis to be made
available on the web, via the University’s digital research repository, the
Library catalogue, the Australasian Digital Theses Program (ADTP) and also
through web search engines, unless permission has been granted by the
University to restrict access for a period of time.
Md. Ayub
iii

Acknowledgements
I would like to express my sincere gratitude to all the people that have made
a contribution to the work presented in this thesis. Without their generous
supportsIwouldhavenotbeenabletofinishthisthesis.Iwouldliketothank
my supervisors Associate Professor Anthony Zander, Professor Benjamin
Cazzolato, Associate Professor Carl Howard, and Dr David Huang, who
in spite of their tremendous work pressure always extended their helping
hand whenever I wanted. I am indebted to my supervisors for proof-reading
this thesis during their busy schedules and their insightful comments which
helped me to improve the overall quality of the work presented in this
thesis. I am grateful to my principal supervisor Associate Professor Anthony
Zander for providing me the opportunity to work in the beautiful work
environment of AVC (Acoustics, Vibration and Control) group, in the school
of mechanical engineering at the University of Adelaide. I would also like
to acknowledge Anthony for assigning me this challenging project that
helped me to learn a completely different side of acoustics engineering
especially acoustic modelling using molecular simulation methods. I am
indebted to Anthony for his generous financial support through a short-
term scholarship and tuition fee waiver during my difficult times when
my postgraduate scholarships were expired. I would like to acknowledge
the efforts of the people from mechanical workshop who fabricated my
experimentalrig(impedancetube)andthepeoplefromelectronicsworkshop
Mr Philip Schmidt, Mr Derek Franklin, Mr Silvio De leso, and Ms Lydia
Zhang, who helped me with my experimental work. A special thanks to Dr
Erwin Gamboa for providing me the access to Materials lab for using fume
hood.
This research was supported under Australian Research Council’s Dis-
covery Projects funding scheme (project number DP130102832). I would like
to thank Prof. Vesselin Shanov, Dr Noe Alvarez and Prof. Mark Schulz of
Nanoworld Laboratories (University of Cincinnati, USA), Professor Stephen
Hawkins and Dr Chi Huynh from CSIRO (Commonwealth Scientific and In-
v
vi Acknowledgements
dustrial Research Organisation, Australia) for providing the carbon nanotube
samples. I would also like to acknowledge the financial support provided by
the University of Adelaide through an International Postgraduate Research
Scholarship (IPRS) and an Australian Postgraduate Award (APA).
I am also thankful to my colleagues Jesse Coombs, Alireza Ahmadi,
Chenxi Li, Cristobal Gonzalez, Maung Myo and Hywel Bennett for their help
andsupport. Iwouldlike toacknowledgeJesse’s contributionforhelpingme
to learn the computation issues. The assistance of Mr Hywel Bennett with
the experiments is also greatly appreciated. I would also like to acknowledge
eResearchSAforcomputationalsupportandtechnicalhelpprovidedbytheir
support team.
A huge thanks to my Bangladeshi friends and brothers Rahul bhai, Tapu
Bhai, Milton Bhai, Mahid Bhai, Numan Bhai, Rumman, Manab, Rabiul Bhai,
Kingshuk,Hassan,Javed,Suvro,Suzon,Sayem,Rifa,Mashuq,andNafeesfor
sharing many happy moments, for their company to make my life enjoyable,
andtoleratingmyfrustrationswhilewritingmythesis.Iamreallygratefulto
you guys for your help, support and encouragement. I would like to express
my sincere thanks to Zahid Bhai and Salma Vabhi for their support during
my stay in their house.
Finally, my sincere gratitude and thanks to my parents, family members,
andfriendsbackinBangladeshfortheirsacrificeandendlesssupportduring
my stay in Australia. I am indebted to my best friend Mohibul Alam for his
financial support and other responsibilities he took for my family over the
years during my postgraduate studies.
Contents
Summary i
Declarations iii
Acknowledgements v
List of Figures x
List of Tables xix
List of Abbreviations xxi
1 Introduction 1
1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Noise Control using Nanomaterials . . . . . . . . . . . . . . . 1
1.3 Overview of the Research . . . . . . . . . . . . . . . . . . . . . 5
1.4 Research Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.5 Chapter Outline . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2 Literature Review 13
2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.2 Nanoscopic Fibres: Carbon Nanotubes . . . . . . . . . . . . . . 13
2.3 Acoustic Absorption Mechanisms . . . . . . . . . . . . . . . . 17
2.4 Numerical Models: Continuum vs Non-Continuum Methods 20
2.5 Non-continuum Methods: Molecular Simulation Models . . . 24
2.6 Capability Requirements of the Methods . . . . . . . . . . . . 32
2.7 Justification of the Methods: LBM, DSMC and MD . . . . . . 34
2.8 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3 Acoustic Absorption Behaviour of a CNT Forest 39
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3.2 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
vii
viii CONTENTS
3.3 Materials and Methods . . . . . . . . . . . . . . . . . . . . . . . 41
3.4 Results and Observations . . . . . . . . . . . . . . . . . . . . . 50
3.5 Absorption Behaviour of a Long CNT Forest . . . . . . . . . . 60
3.6 Difficulties and Limitations in CNT Sample Preparation . . . 71
3.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
4 Acoustic Simulation of Nano-channels using MD 75
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
4.2 Basics of Molecular Dynamics . . . . . . . . . . . . . . . . . . . 75
4.3 Simulation Tools: LAMMPS, VMD, Tcl Script, TopoTools . . . 91
4.4 Implementation of MD for Nano-channel Flow and Acoustics
Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
4.5 Potential Cases for MD Simulation of Acoustic Absorption
Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
4.6 Limitations of MD simulation in Audible Frequency Range . 101
4.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
5 Validation Cases for MD Simulation 105
5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
5.2 Nanoscale Fluid/Structure Interaction . . . . . . . . . . . . . . 107
5.3 Thermal Boundary Resistance . . . . . . . . . . . . . . . . . . . 114
5.4 Sound Wave Propagation in a Gas . . . . . . . . . . . . . . . . 120
5.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
6 Sound Propagation & Classical Absorption in a Gas 133
6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
6.2 Simulation Details . . . . . . . . . . . . . . . . . . . . . . . . . 136
6.3 Theory: Calculation Methods . . . . . . . . . . . . . . . . . . . 137
6.4 Sanity Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146
6.5 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . 156
6.6 Attenuation of Sound in the Fluid Medium . . . . . . . . . . . 172
6.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178
7 Sound Propagation in a Gas in Presence of a CNT 179
7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179
7.2 Simulation Details . . . . . . . . . . . . . . . . . . . . . . . . . 180
7.3 Attenuation due to the Presence of a CNT: Calculation Methods182
7.4 Observations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188
7.5 Simulation Results and Discussions . . . . . . . . . . . . . . . 193
7.6 Effects on CNT . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
7.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211